From: Pit Capitain <pit@...>
Date: 2007-03-14T16:52:49+09:00
Subject: Re: Where is my Class ?

sur max schrieb:
> assignment happened LEFT-to-RIGHT
> 
>> a = Class.new
>> #  #<Class:0x2de1f00>
>>
>> B = Class.new
>> # B
>>
>> B=a
>> it gives
>> # warning: already intialized constant B .... thats fine
>>
>> but
>> and now if i check a as
>>
>> a
>> # B
>>
>> so where is the original class of a that was #<Class:0x2de1f00> .... and
>> how
>> come the assignment happens from RIGHT-to-LEFT ?
>>
>> any idea ?

sur max, you still have the same class, accessible via both a and B:

   a = Class.new  # => #<Class:0x310b640>
   a.object_id    # => 25713440

   B = Class.new  # => B
   B.object_id    # => 25706400

   B = a          # warning: already initialized constant B
                  # => B
   a              # => B
   a.object_id    # => 25713440
   B.object_id    # => 25713440

The reason is that Ruby uses the name of the first constant a class 
object is assigned to as the class' name:

   X = Class.new  # => X
   Y = X          # => X
   Y              # => X

In your case, you created an "anonymous" class without assigning it to a 
constant, so it doesn't have a name yet. After assigning this anonymous 
class to the constant B, you get the warning, but nethertheless the 
constant is changed to reference the previous anonymous class. After the 
assignment, the class isn't anonymous anymore, it has got the name "B".

This way you can create multiple classes with the same name:

   c1 = Class.new  # => #<Class:0x30f60c4>
   c2 = Class.new  # => #<Class:0x30f3aa4>

   C = c1          # => C
   C = c2          # warning: already initialized constant C
                   # => C

   c1              # => C
   c2              # => C

They still are distinct classes, though.

   c1.object_id    # => 25669730
   c2.object_id    # => 25664850

Regards,
Pit